1. Field of the Invention
The present invention relates to display devices, and more particularly to a display device with a driving circuit including a single channel bidirectional shift register.
2. Description of the Related Art
In recent years, active-matrix liquid crystal display devices that use thin-film transistors (TFTs) as their active elements have been employed in digital still cameras, cell phones, and the like.
In these configurations, digital still cameras, cell phones, and the like may require a liquid crystal display panel that enables bidirectional display.
For a liquid crystal display panel enabling bidirectional display mentioned above, it is considered to provide a technique for incorporating two shift registers: a shift register for forward scanning and a shift register for reverse scanning, like a forward vertical scanning circuit 10 and a reverse vertical scanning circuit 20 included in a liquid crystal display panel 30 shown in FIG. 18.
In this technique, however, the circuit scale is almost doubled and this results in reduced yield, so it becomes necessary to reduce the circuit scale if an additional circuit is required in the future.
In general, a CMOS shift register has a single input (IN) and a single output (OUT) per stage as shown in FIG. 19A. As shown in FIG. 19B, therefore, bidirectional scanning control can be realized with a single circuit at one side in a simple circuit configuration which employs signal routing switch elements (F, R).
However, a single channel shift register using N-type MOSFETs, for instance, has three inputs (IN, SET, and RESET) and a single output (OUT) per stage as shown in FIG. 20A. In addition, since the single channel shift register further requires a preceding stage and a following stage, a bidirectional circuit configuration with signal routing switch elements (F, R) becomes complex and increases in the number of elements required, as shown in FIG. 20B.
Literature on conventional techniques relating to this Application includes the following:
[Patent Document 1]
Japanese Patent Laid-Open No. Hei 07-13513
]Patent Document 2]
Japanese Patent Laid-Open No. 2002-215118